Polarization Property Associated with Surface Plasmon Resonance in a Palladium Thin-Film Coated Aluminum Grating in a Conical Mounting and Its Application to Hydrogen Gas Detection.

We have investigated a polarization property of the (specularly) reflected light from an aluminum grating, coated with a palladium (Pd) thin-film on its surface. The polarization property, which is associated with surface plasmon resonance (SPR), and occurs in the Pd thin-film on the aluminum grating in a conical mounting, is observed as a rapid change in the normalized Stokes parameter s3, around the resonance angle, θsp, at which point, SPR occurs. The sensing technique used the rapid change in s3 to allow us to successfully detect a small change in the complex refractive index of the Pd thin-film layer upon exposure to hydrogen gas, with a concentration near the lower explosion level. Experimental results showed that the sensing technique provided a sensitive and stable response when the Pd thin-film layer was exposed to gas mixtures containing hydrogen at concentrations of 1 to 4% (by volume) in nitrogen.

Rapid change in polarization accompanying Fabry-Pérot resonance in anodic porous alumina coated with a gold thin film.

We experimentally investigate the polarization property of the specularly reflected light from an anodic porous alumina (APA) membrane coated with a gold (Au) thin film. As a result, we reveal a rapid change in the normalized Stokes parameter s 3 of the specularly reflected light around the angle of incidence θ A at which the resonance absorption of the incident light occurs. The rapid change in s 3 demonstrates that the specularly reflected light can rapidly be right- to left-elliptically polarized via linear polarization at the zero-crossing point θ Z of s 3. Moreover, θ Z is located close to θ A , and θ Z as well as θ A depend on the occurrence conditions of the resonance absorption. From numerical aspects based on the Maxwell Garnett effective medium approximation, we clarify that the rapid change in s 3 accompanies the Fabry-Pérot (FP) resonance in the Au-coated APA membrane. The numerical results also suggest that the change in the refractive index of the filling material into nanopores of the Au-coated APA membrane can be successfully estimated by using the rapid change in s 3.